I can't speak to how Marriott works, but the hotel group I worked for blocked this sort of editing by design.

When a reservation is booked through a travel agency (TA), that agency "owns" the reservation. All changes must be done through that TA. This is done for two reasons.

First, if changes are made directly by the guest, the reservation that's in the chain's computer will no longer be identical to what's in the TA's computer. When reservations are out of sync, it becomes impossible to know which is the most accurate. So, reservation changes were blocked for anyone except the TA and the hotel.

Second, many reservations booked by TAs are commissionable. A decent TA will have a master list of expected commissions. If what they receive differs from the expected, they will dispute the commission. When that happens, the hotel must investigate the discrepancy. That process takes time, which is a labor cost. One of the ways to avoid this cost is to block the guest from making changes to the reservation.

[QUOTE=AHC96;32734467]Rang the normal Marriott reservations to check if they could do anything and the agent was as confused as me, without being able to edit the reservation. Her suggestion was to wait until I check in to show the member card and for them to add it manually there.

You may have gotten an informed agent. Again, maybe Marriott is different, but the industry standard is to refer guests back to their travel agent to make any changes.

(I know that adding a Marriott frequent guest reward number won't have any actual affect on the reservation in terms of confusion and/or commission. But, the chains I've worked with all had a "all changes must go through the TA" policy and not a piecemeal one where some changes are okay and others are not. It's just easier to refer the guest back to the TA for everything. And since the hotel group is paying a commission (usually), they will try to push any labor costs back to the TA.)